A/C SYSTEM GENERAL DIAGNOSTIC PROCEDURES
1983-90 AIR CONDITIONING & HEAT General Servicing Diagnostic Procedures
ALTITUDE PRESSURE VARIATIONS

NOTE: Diagnosis is an important first step in A/C system servicing. To save time and effort, systems should be carefully checked to identify the causes of poor performance. By using the following diagnostic charts, defective components or system damage can be quickly located. To identify problems that are specific to one system, refer to the repair section of this manual. The charts in this section apply to all systems.

ALTITUDE PRESSURE VARIATIONS
Altitude (Ft. Above Sea Level) Absolute Pressure of Atmosphere (psi) (1) Gauge Altitude Correction (psi)
0 14.7 0
1000 14.2 -0.5
2000 13.7 -1.0
3000 13.2 -1.5
4000 12.7 -2.0
5000 12.2 -2.5
6000 11.7 -3.0
7000 11.3 -3.4
8000 10.9 -3.8
9000 10.5 -4.2
10,000 10.1 -4.6
(1) Subtract correction shown from gauge readings.
ALTITUDE VACUUM VARIATIONS

ALTITUDE VACUUM VARIATIONS
Altitude (Ft. Above Sea Level) Absolute Pressure of Atmosphere (psi) (1) Gauge Altitude Correction (psi)
0 29.92 0
1000 28.92 +1.0
2000 27.82 +2.1
3000 26.82 +3.1
4000 25.82 +4.1
5000 24.92 +5.0
6000 23.92 +6.0
7000 23.02 +6.9
8000 22.22 +7.7
9000 21.32 +8.6
10,000 20.52 +9.4
(1) Add correction shown to gauge readings.
PREPARATION FOR TESTING

1. Attach Low and High pressure gauges.
2. Start engine and allow to warm up.
3. Set system to "COOL" and blower to "HIGH".
4. Open car doors and hood.
5. Run engine at fast idle for 2-3 minutes.

Fig. 1: AIR CONDITIONING SYSTEM PERFORMANCE CHECK TABLE

Fig. 2: Ambient Temperature/Pressure A/C Chart

Fig. 3: Evaporator Temperature/Pressure A/C Chart

AIR CONDITIONING DIAGNOSIS WITH GAUGES FOR SYSTEMS WITH INSUFFICIENT OR NO COOLING
LOW SIDE GAUGE HIGH SIDE GAUGE OTHER SYMPTOMS (1) DIAGNOSIS
Normal Normal No or few bubbles in sight glass. High side gauge may go high. Low side gauge does not fluctuate with compressor on/off cycle. Some Air and Moisture in System.
Normal Normal Cools okay in morning but not during hot part of day. Tiny bubbles in sight glass. Discharge air warm when low side gauge drops into vacuum. Excessive Moisture
Normal Normal Thermostatic switch system only-compressor cycles off and on too rapidly. Cycling clutch systems only-Compressor doesn't turn on soon enough. Defective Thermo- static Switch
Normal Normal Discharge air becomes warm as low side pressure rises. Misadjusted Thermo- static Switch or Defective Pressure Sensing Switch
Low Low Bubbles in sight glass. Outlet air slightly cool. Low R-12 Charge
Low Low Sight glass clear or oil- streaked. Outlet air very warm. Excessively Low R-12 Charge
Low Low Outlet air slightly cool. Sweating or frost at at expansion valve. Expansion Valve Stuck Closed. Screen Plugged or Sensing Bulb Malfunction.
Low Low Low High Outlet air slightly cool. High side line cool to touch. Sweating or frost on high side. Evaporator outlet pipe cold. Low side goes into vacuum when blower is disconnected. Restriction on High Side STV Stuck Open
High Low Evaporator outlet pipe warm. Outlet air warm. STV Stuck Open
High Low Noise from compressor. Compressor Malfunction
High High Outlet air warm. Liquid line very hot. Bubbles in sight glass. Condenser Malfunction or R-12 Overcharge.
High High Outlet air slightly cool. Bubbles in sight glass. Large Amount of Air and Moisture in System.
High High Outlet air warm. Evaporator outlet sweating and frost. Expansion Valve Stuck Open
(1) If equipped with a low refrigerant charge protection system, compressor operation may have stopped.